1. Field of the Invention
The present invention relates to a geomagnetic sensor and an azimuth calculation method medium thereof. More particularly, the present invention relates to a geomagnetic sensor precisely calculating a pitch angle and a roll angle according to a region using 3-axis acceleration sensors to calculate an azimuth and an azimuth calculation method and medium thereof.
2. Description of the Related Art
A geomagnetic sensor is a device measuring the intensity and direction of geomagnetism, which a human can not feel, and more particularly, a sensor measuring the geomagnetism using a flux gate is called a flux gate geometric sensor.
The flux gate geometric sensor is a device measuring the intensity and direction of an external magnetic field by using a high permeability material such as permalloy as a magnetic core, adding excitation magnetic field through a coil winding the magnetic core, and measuring second harmonic component proportional to the external magnetic field generated according to magnetic saturation of the magnetic core and non-linear magnetic features. The flux gate geometric sensor was developed in the late 1930s and is good in sensitivity, cost-effective and miniaturized, compared with many kinds of other geomagnetic sensors.
Especially, as a micro electro mechanical system (MEMS) technology is nowadays developing, a micro flux gate sensor with low power consumption can be equipped in various portable electronic devices including a cell phone, personal digital assistant (PDA) and laptop computer using the technology.
Meanwhile, the geomagnetic sensor generally uses a 2 or 3 axis flux gate. When an azimuth is measured using the geomagnetic sensor, if the geomagnetic sensor is tilted, the azimuth can be miscalculated. Accordingly, an algorithm compensating the azimuth using a tilt angle, that is, a pitch angle and a roll angle is generally performed. Therefore, a conventional geomagnetic sensor calculates the pitch angle and the roll angle using 2-axis acceleration sensors to compensate the azimuth. In this case, the range of measuring a tilt is limited to ±90°.
In addition, the conventional geomagnetic sensor calculates the pitch angle and the roll angle by applying a function of sin−1 ( ) to a value of X axis and a value of Y axis of the acceleration sensor. However, if the tilt is over 60°, the tilt of a signal gets flat because of the nature of a sine function. In this case, if the resolving power of an analog to digital converter (ADC) converting an output value of the acceleration sensor into a digital value is not high enough, a tilt angle can not precisely be acquired. Specifically, if the tilt is over +90°, for example, if the tilt is 120°, +60° instead of +120° is recognized.
So, if an error occurs in the calculated pitch angle value and roll angle value, azimuth compensation does not work well so that the azimuth itself is miscalculated.